Known as examples of conventional open X-ray sources are those described in Patent Literatures 1 to 3. Each of the open X-ray sources described in Patent Literatures 1 to 3 comprises an electron source for emitting an electron beam, a target for generating an X-ray in response to the electron beam incident thereon, an electron path, extending from the electron source to the target, for transmitting the electron beam therethrough, and an electromagnetic coil arranged so as to surround the electron path. These open X-ray sources can open and close the electron path with respect to external atmospheres and vacuum the electron path when closed.
The open X-ray sources described in Patent Literatures 1 to 3 use cooling structures for cooling their targets and electromagnetic coils with water. This inhibits the X-ray from shifting its focal point due to thermal expansions of members constituting the open X-ray sources at the time when they operate and thereby deteriorating characteristics.